The numbers look random but they're actually designed so that the aperture area of the lens with the next f-stop is half of the area of the one that comes before.

<aside> 💡 This only applies to lenses that "jumps" or "clicks" between aperture stops, not to lenses with smooth aperture transition like my Meike 35mm f/1.7 (YouTube review).


<aside> 💡 Some manufacturers also produce lenses with half (i ∈ {1, 1.5, 2, 2.5, ...}) or third stop (i ∈ {1, 1.33, 1.67, 2, ...}) jumping capability so you get numbers like 1.7 (i = 2.5) or 1.1 (i = 1.33).


Some open questions I don't have the time to research yet

Further reading